A conventional structure of an electric motor used in a vehicle is noise-prone, i.e., a gap between a coil of the motor and a motor case serving as a capacitor to generate a noise. Such a noise may be prevented by the following structure. For example, in a patent document, Japanese Patent Laid-Open No. H4-355602A, (Patent document 1) the generated noise is released via a common mode path, which is provided as a connection of the motor parts and the vehicle body, that is, a grounding of the motor case and a heat sink to a vehicle body frame.
In the patent document 1, the noise affecting the controller is reduced by connecting the motor case and the heat sink to the vehicle body frame, and, as a trade-off, the noise leaking out from the motor increases. Further, the noise leaking out from the motor case and the heat sink of the motor is a common mode noise, and there is no knowledge about what path such a noise takes toward an outside of the motor. Therefore, the noise leaking out from the motor case and the heat sink of the motor is transmitted to an antenna of a radio, and to a communication device, etc., which may cause a radio noise.